Conduction heating apparatus and hot press forming apparatus having the same, and conduction heating method

ABSTRACT

A conduction heating apparatus performs conduction heating while clamping a work to be hot press-formed by a clamping mechanism to apply tension to the work. The clamping mechanism has a stationary clamping member and a movable clamping member, a lifting up/down cylinder for the stationary clamping member and the movable clamping member, and tensioning cylinders that drive the movable clamping member along the planar direction of the work, and in conduction heating. The stationary clamping member clamps one side of the work and hold it, and the movable clamping member moves while holding the other side of the work according to thermal deformation of the work, which applies tension to the work corresponding to the thermal deformation of the work.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is based on and claims the benefit of the priorityof Japanese Patent Application No. 2007-322507 (filed on Dec. 13, 2007),and the disclosure of which is incorporated herein in its entirety byreference thereto.

TECHNICAL FIELD

The present invention relates to a conduction heating apparatus and ahot press forming apparatus having the conduction heating apparatus, andfurther to a conduction heating method. In particular, the presentinvention relates to a conduction heating apparatus built in a hot pressforming apparatus, and a conduction heating method executed in the hotpress forming apparatus.

BACKGROUND

As one of the methods of mass-producing vehicle parts requiringhigh-strength, a hot press forming technique or a die quenchingtechnique is employed. The die quenching technique is a technique inwhich a steel plate is heated to at approximately 900° C., and the steelplate is thereafter rapidly cooled simultaneously with press forming, toquench a formed product. Further, for the heating of a steel plate,conventionally, a continuous heating furnace installed separately fromthe press forming apparatus is generally used.

On the other hand, in Patent Document 1, there is disclosed a hot pressforming method using a conduction heating mechanism for heating a steelplate. In detail, in Patent Document 1, there is disclosed the hot pressforming method for a metal plate comprising the successive steps of“respectively attaching electrodes to one or more places of the bothends of a metal plate inside a metal die or in the vicinity of the dieoutside the metal die, applying an electric current between theelectrodes to heat the metal plate to at a predetermined processingtemperature by Joule heat, and performing hot press forming”.

The conduction heating mechanism in Patent Document 1 has a pair ofright and left clamping electrodes moving along a longitudinal directionof a work, and the pair of right and left clamping electrodesrespectively clamps the both ends in the longitudinal direction of thework during conduction heating, to apply pulling force to the work inthe right and left directions along the longitudinal direction of thework. The pair of right and left clamping electrodes is out of movementduring conduction heating and a distance between the right and leftclamps is fixed.

Patent Document 1: Japanese Patent Kokai Publication No. JP-P2002-18531A

SUMMARY

The disclosure in Patent Document 1 described above is hereinincorporated by reference. The analysis set forth below is given by thepresent invention.

According to the conduction heating mechanism of Patent Document 1,there is a problem that the work is greatly distorted and the centralportion of the work droops down regardless of an application of pullingforce to a work during conduction heating.

The reason for the problem is that a clamping distance between the pairof right and left clamps is fixed regardless of the fact that a workexpands according to a temperature rise during conduction heating. Thatis, since the both ends of the work are restrained at the fixedpositions in conduction heating, as a result, the central portion of thework easy to be thermally deformed due to a temperature rise droops downby its own weight.

Therefore, according to the conduction heating mechanism in PatentDocument 1, it is difficult to stably supply a work to the downstreamsteps of conduction heating. The reason for that is that, since adistortion of a work due to conduction heating is great, it is difficultto perform positioning of the work, and the greatly distorted portionthereof may interfere with the holding members of a conveying mechanismor a die of a hot press mechanism.

It is an object of the present invention to provide a conduction heatingapparatus which is capable of preventing a distortion of a work due toconduction heating as much as possible, and stably supplying aconduction heated work to the downstream steps of conduction heating,and a hot press forming apparatus having the conduction heatingapparatus, and a conduction heating method.

According to a first aspect of the present invention, there is provideda conduction heating apparatus that performs conduction heating onto awork to be hot press formed while clamping the work by a clampingmechanism under application of tension to the work, in which theclamping mechanism comprises: a stationary clamping member which clampsone side of the work to be free to hold the one side of the work, and isfixed in position or capable of being freely fixed in position along apredetermined direction, and a movable clamping member which clamps theother side of the work to be free to hold the other side of the work,and is free to move along the predetermined direction; and in conductionheating, the stationary clamping member holds the one side of the workat a fixed position, and the movable clamping member moves along thepredetermined direction while holding the other side of the workaccording to a thermal deformation along the predetermined direction ofthe work, which applies tension to the work. The predetermined directionis a principal direction in which the work is easy to expand due to athermal deformation, and is the same direction as a longitudinaldirection of the work, or a direction along the upper and lower planesor the pressing plane of the work, for example.

According to a second aspect of the present invention, there is provideda conduction heating apparatus that performs conduction heating onto awork to be hot press formed while clamping the work by a clampingmechanism under application of tension to the work, in which theclamping mechanism comprises: first and second clamping members thatclamp the work at different clamping positions respectively, to applytension to the work; a clamping direction driving mechanism driving thefirst and second clamping members to clamp the work; and a clampingdistance varying mechanism varying a clamping distance between the firstand second clamping members according to a thermal deformation of thework upon conduction heating.

According to a third aspect of the present invention, there is provideda hot press forming apparatus comprising: the conduction heatingapparatus according to the present invention; and a hot press mechanismthat hot press-forms the work heated by the conduction heatingapparatus.

According to a fourth aspect of the present invention, there is provideda conduction heating method for performing conduction heating onto awork to be hot press-formed while clamping the work under application oftension to the work, the method comprising: a clamping step of applyingtension to the work while clamping one side and the other side of thework respectively to hold the work; a conduction heating step ofperforming conduction heating onto the clamped work; and a tensionapplying step during conduction heating of clamping the one side of thework at a fixed position and moving the other clamping position of theother side of the work along with the work subject to be thermallydeformed, to apply tension to the work upon the conduction heating.

According to the present invention, during the conduction heating, aclamping position at which the work is held or a clamping distancethereof is moved or varied along with the work that will be thermallydeformed preferably according to an amount of the thermal deformation ofthe work, in particular, according to thermal expansion or stretchthereof. Thereby appropriate tension is applied to the work duringconduction heating, to prevent a distortion of the work due to atemperature rise, in particular, to prevent the central portion of thework from greatly drooping, which keeps the work in a flat state as muchas possible. As a result, in the case where the conduction heated workis conveyed to the hot press mechanism on the downstream side,interference of the work with the components of the conveying mechanismor the hot press mechanism is prevented.

According to the present invention, during conduction heating, one sideof a work is clamped at a fixed position by the stationary clampingmember. Thereby preventing a shift in position for work positioningcaused by a thermal deformation of the work or a movement of the movableclamping member. As a result, in the case where the conduction heatedwork is conveyed to the hot press mechanism on the downstream side, itis easy to deliver the work to the conveying mechanism or the hot pressmechanism, and which makes work positioning easy in the hot pressforming step. Thus the conduction heated works are stably supplied.

In this way, the present invention by which it is possible to stablysupply a conduction heated work to the downstream step, contributes tohot press forming, in particular, making the die quenching intohigh-cycle. Further, in the case where the clamps serve as electrodes aswell, as described above, according to the present invention, since awork is kept in a flat state as much as possible in the conductionheating, uniform heating for the work is expected.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is an appearance diagram of a hot press forming apparatus intowhich a conduction heating apparatus is built, according to an Exampleof the present invention.

FIGS. 2A to 2C are diagrams of three planes for explanation of amechanical structure of the conduction heating apparatus and the hotpress forming apparatus shown in FIG. 1. FIG. 2A is a top plan viewthereof, FIG. 2B is a front view thereof, and FIG. 2C is a side viewthereof.

FIG. 3 is an enlarged view of FIG. 2C.

FIG. 4 is a block diagram for explanation of a control configuration ofthe conduction heating apparatus shown in FIG. 3.

(A) to (F) of FIG. 5 are process drawings for explanation of operationsof the conduction heating apparatus shown in FIGS. 3 and 4.

FIG. 6 is a process drawing for explanation of a problematic point of aconduction heating apparatus according to a comparative example in whicha clamping distance L is fixed.

As for explanation of signs, refer to the end of the description.

PREFERRED MODES

According to a preferred exemplary embodiment of the present invention,the clamping mechanism has a lifting up/down direction driving mechanismthat drives the stationary clamping member and the movable clampingmember to freely lift up/down along a thickness direction of the work,to clamp the work, and a movable clamping member driving mechanism thatdrives the movable clamping member to freely move along thepredetermined direction.

According to a preferred exemplary embodiment of the present invention,the stationary clamping member and the movable clamping memberrespectively have pairs of upper and lower clamps facing each otheralong the thickness direction of the work to freely pinch the work.According to this aspect, clamping of the work is made stable, and it iseasy to secure a moving stroke of the movable clamping member.

According to a preferred exemplary embodiment of the present invention,the lower clamps spaced from each other along the predetermineddirection or the longitudinal direction of the work between the pairs ofupper and lower clamps which the stationary clamping member and themovable clamping member respectively have, are a pair of electrodes forenergizing the work. According to this aspect, power saving, downsizingof the mechanisms, and uniform heating for the work are expected.

According to a preferred exemplary embodiment of the present invention,the stationary clamping member and the movable clamping memberrespectively have pairs of upper and lower clamps facing each otheralong the thickness direction of the work to freely pinch the work, andportions of the upper clamps pinching the work are of convex curvedshapes, and portions of the lower clamps pinching the work are of planarshapes. According to this aspect, clamping is made stable. Further, inthe case where the clamps serve as electrodes as well, the electrodesare prevented from unevenly abutting to the work, which prevents localoverheating in the work.

According to a preferred exemplary embodiment of the present invention,the apparatus comprises a droop preventing member which is disposedbeneath a central portion of the work during conduction heating, thedroop preventing member freely support the central portion. It is morepreferable that the droop preventing member is a plurality of pinsprovided upright along the vertical direction. According to such anaspect, without interfering with supplying of a work to the conductionheating apparatus or discharging thereof to the downstream side, it ispossible to prevent or restrain a droop of the central portion of thework in conduction heating.

According to a preferred exemplary embodiment of the present invention,the clamping mechanism has clamps or clamps serving as electrodes aswell for elastically clamping the work. It is more preferable that theclamping mechanism has supporting member(s) or supporting pillar(s) towhich the clamp(s) or the clamp(s) serving as electrode(s) as well areattached, and the supporting member(s) include base portion(s),attachment portion(s) which is (are) directly or indirectly connected tothe base portion(s) and to which the clamp(s) or the clamp(s) serving aselectrode(s) as well are attached, and elastic portion(s) which is (are)directly or indirectly inserted between the base portion(s) and theattachment portion(s) so as to exert elastic force along the clampingdirection between the base portion(s) and the attachment portion(s).According to this aspect, a contacting area between the clamp(s) and thework is increased, and a uniform clamping load is exerted onto the work,thereby stabilizing the clamping, and increasing a contacting areabetween the electrode(s) and the work, which prevents local overheatingin the work.

In a preferred exemplary embodiment of the present invention, itsuffices to perform conduction heating so as to heat the work up to atemperature possible for hot pressing. For example, in the case of steelworks, it suffices to perform conduction heating between an A1transformation temperature and a liquid-phase precipitation temperature,for example, from 850 to 1,200° C.

The present invention is suitably applied to heating and furtherheat-forming of works of various materials which can be subjected toconduction heating and hot processing, and in particular, to diequenching. For example, the present invention is suitably applied toforming steel system, aluminum system, and other various metalmaterials. The present invention is suitably applied to heating and, inaddition, hot forming of not only general steel plates, but also platedsteel plates (for example, galvanized steel plates, alloyed fused zinchot dip galvanized steel plates, aluminum plated steel plates, and thelike).

EXAMPLES

Hereinafter, an example of the present invention will be described withreference to the drawings. FIG. 1 is an appearance diagram of a hotpress forming apparatus into which a conduction heating apparatusaccording to an example of the present invention is built.

Referring to FIG. 1, in a hot press forming apparatus 1, a conductionheating apparatus 3 to which works are supplied one by one from arobotic type feeding mechanism 2, a die quenching hot press mechanism 4disposed so as to be thermally isolated on the downstream side of theconduction heating apparatus 3, and a transfer mechanism 5 that at leastcarries a conduction heated work from the conduction heating apparatus 3to the hot press mechanism 4 and carries a formed product from the hotpress mechanism 4 to a discharging position are built into the apparatus1. Note that a conveying conveyor 7 for discharging a formed product ora completed article from the discharging position of the apparatus 1 isadditionally installed in the hot press forming apparatus 1.

The work feeding mechanism 2 is a robotic mechanism, and takes out worksone by one from a magazine in which a plurality of works or blanks arecontained, to supply those one by one to the conduction heatingapparatus 3.

The conduction heating apparatus 3 performs clamping of a fed work and areleasing thereof and performs energization (electric conduction) to thework to which tension by the clamping is applied, to heat the work.

The hot press mechanism 4 hot presses and rapidly-cools a heated work toform a formed product from the work.

The transfer mechanism 5 has a plurality of holding mechanisms orholding members that hold works or formed products or release theholdings thereof at a feeding position at which a work is fed into thehot press forming apparatus 1 or the conduction heating apparatus 3, anenergizing position at which the conduction heating apparatus 3energizes (applies electric conduction to) a work, a processing positionat which the hot press mechanism 4 hot press-forms a work, and adischarging position at which a formed product is discharged out of thehot press forming apparatus 1, and respectively reciprocate between thefeeding position and the energizing position, between the energizingposition and the processing position, and between the processingposition and the discharging position.

FIGS. 2A to 2C are diagrams of three planes (views) for explanation ofthe conduction heating apparatus and the hot press forming apparatusshown in FIG. 1. FIG. 2A is a top plan view thereof, FIG. 2B is a frontview thereof, and FIG. 2C is a side view thereof. FIG. 3 is an enlargedview of FIG. 2C. Note that FIG. 2C shows a state in which upper clamps30 a and 31 a are at lifted-up positions, and a movable clamping member31 is moved to the end portion.

Referring to FIGS. 2A to 2C and FIG. 3, in the hot press formingapparatus 1, a feeding position P0 at which a work W is fed, anenergizing position P1 at which conduction heating by the conductionheating apparatus 3 is performed, a processing position P2 at which hotpress forming or die quenching by the hot press mechanism 4 isperformed, and a discharging position P3 at which a formed product isdischarged out of the hot press forming apparatus 1 are set at regularpitches in the order from the upstream side toward the downstream sidealong a conveying direction.

The conduction heating apparatus 3 has a clamping mechanism (30, 31, 32,33 a, 33 b, 34) which will be described later, an energizing mechanism(refer to an energizing mechanism 37 in FIG. 4) having electrodescontacting the work W, wirings for electrically connecting between theelectrodes and an electric power source and an energizing switch, and aplurality of pins 35 serving as droop preventing members which aredisposed beneath the central portion of the work W during conductionheating and provided upright along the vertical direction, to freelysupport the central portion of the work W.

The clamping mechanism (30, 31, 32, 33 a, 33 b, 34) has a stationary(positionally fixed) clamping member 30 and a movable clamping member 31(first and second clamping members), a lifting up/down cylinder 32serving as a lifting up/down direction driving mechanism or a clampingdirection driving mechanism for the stationary clamping member 30 andthe movable clamping member 31, upper and lower tensioning cylinders 33a and 33 b serving as a movable clamping member driving mechanism thatmoves the movable clamping member 31 along the predetermined directionor a clamping distance varying mechanism responding to a thermaldeformation of the work W, and upper and lower translatory guides 34 and34 guiding a movement of the movable clamping member 31.

The stationary clamping member 30 which clamps one side of the work Walong its longitudinal direction or horizontal direction of the work Wat a fixed position to freely hold the same side and has a function ofpositioning the work W as well. The movable clamping member 31 clampsthe other side of the work W to freely hold the other side and to freelymove along the predetermined direction or the horizontal direction. Inconduction heating, the stationary clamping member 30 holds the one sideof the work at the fixed position, and on the other hand, the movableclamping member 31 moves while holding the other side of the work Waccording to a thermal deformation of the work W. By the stationaryclamping member 30 and the movable clamping member 31, tension isapplied to the work W so as to prevent the central portion of the work Wfrom drooping as much as possible in conduction heating. In particular,tension acting forward a moving direction of the movable clamping member31 is applied to the work W.

The stationary clamping member 30 and the movable clamping member 31respectively have the pairs of upper and lower clamps 30 a and 30 b, and31 a and 31 b, respectively, facing each other along the thicknessdirection of the work W to freely pinch the work W. The pair of lowerclamps 30 b and 31 b spaced from each other along the longitudinaldirection of the work W among the pairs of upper and lower clamps 30 aand 30 b, and 31 a and 31 b which the stationary clamping member 30 andthe movable clamping member 31 respectively have, is a pair ofelectrodes for energizing (applying electric current conduction to) thework W.

The lifting up/down cylinder 32 drives the upper clamps 30 a and 31 a ofthe stationary clamping member 30 and the movable clamping member 31 tofreely lift up/down (ascend/descend) along the thickness direction ofthe work W, to clamp the work W and hold it. The upper and lowertensioning cylinders 33 a and 33 b drive the movable clamping member 31to freely move along the predetermined direction, i.e., the longitudinaldirection or horizontal direction of the work W. The upper and lowertensioning cylinders 33 a and 33 b exert a biasing force to the movableclamping member 31 in order for the movable clamping member 31 not toslide along the work W at the time of moving the movable clamping member31 in conduction heating. Note that the stationary clamping member 30 isprovided fixedly (stationarily) in position along the predetermineddirection, or provided so as to be capable of varying its initialposition according to a shape of the work W by an air cylinder, a motor,or the like.

The clamps 30 a, 30 b, 31 a, and 31 b are respectively attached to theend portions of upper and lower support pillars 39 a and 39 b. The uppersupport pillars 39 a and 39 a are attached to an upper frame 38 a whichis free to lift up/down, and the upper frame 38 a is connected to thelifting up/down cylinder 32. The lower support pillars 39 b and 39 b areattached to an immobile lower frame 38 b. The upper and lowertranslatory guides 34 and 34 and the tensioning cylinders 33 a and 33 bare respectively disposed onto the upper and lower frames 38 a and 38 b.Note that it is possible to drive the upper and lower clamps 31 a and 31b of the movable clamping member 31 with one cylinder or the like.

The hot press mechanism 4 has a cooling die 41 for performing hotpressing to rapidly cool the work conveyed from the energizing positionP1 by the transfer mechanism 5, at the processing position P2 after thework W is conduction heated at the energizing position P1.

The transfer mechanism 5 has a pair of parallel arms 51 extending alongthe conveying direction of the work W, cylinders (not shown) serving asdriving means that drive the pair of parallel arms 51 to freely move ina reciprocating manner along the conveying direction, a lifting up/downdirection perpendicular to the conveying direction, and a widthdirection perpendicular to the conveying and lifting up/down directions,and a plurality of clamps (not shown) serving as holding mechanisms orholding members which are attached plurally to the pair of parallel arms51 at predetermined intervals along the conveying direction, and hold awork W or a formed product when the pair of parallel arms 51 approacheseach other along the width direction, and release the holding when thepair of parallel arms 51 is separated from each other. The plurality ofclamps are disposed at regular pitches on the pair of parallel arms 51so as to correspond to the distances between the feeding position P0,the energizing position P1, the processing position P2, and thedischarging position P3. Note that a servo motor or the like may beemployed as driving means in place of the cylinders serving as drivingmeans.

Moreover, the transfer mechanism 5 has a support rod 54 that supports orguides a work W thermally deformed such that its central portion droopsdue to conduction heating between the energizing position P1 and theprocessing position P2. The support rod 54 is inclined so as to behigher toward the downstream side in the conveying direction such thatthe side of the processing position P2 is made higher than the side ofthe energizing position P1. The inclined angle of the support rod 54 isset in accordance with a material of works W, a heating temperature, anda stroke width in the lifting up/down direction of the transfermechanism 5.

FIG. 4 is a block diagram for explanation of a control configuration ofthe conduction heating apparatus 3 shown in FIG. 3. Referring to FIG. 4,the conduction heating apparatus 3 comprises the stationary clampingmember 30 and the movable clamping member 31 (first and second clampingmembers), the lifting up/down cylinder 32, the upper and lowertensioning cylinders 33 a and 33 b, a current sensor 36 a detecting anamount of electric current applied to a work W, a temperature sensor 36b detecting a temperature of the work, a lifting up/down position sensor36 c detecting positions in the lifting up/down direction of thestationary clamping member 30 and the movable clamping member 31, amovable clamping member position sensor 36 d detecting a position in amoving direction position of the movable clamping member 31, theenergizing mechanism 37 controlling energization (electric conduction)to the work W, and a control board (microcomputer) 36 e serving as meansfor controlling the lifting up/down cylinder 32, the upper and lowertensioning cylinders 33 a and 33 b, and the energizing switch 37 a onthe basis of information detected by the sensors 36 a to 36 d. Theenergizing (conducting) mechanism 37 is composed of the pair of lowerclamps 30 b and 31 b serving as electrodes as well, a direct-current oralternating-current power source P, the energizing switch 37 a which isconnected between the direct-current or alternating-current power sourceP and the lower clamps 30 b and 31 b to switch on/off energization(conduction) to a work W, the current sensor 36 a, and the temperaturesensor 36 b.

Next, the operations of the conduction heating apparatus 3 will bedescribed.

(A) to (F) of FIG. 5 are process drawings for explanation of theoperations of the conduction heating apparatus shown in FIG. 3 and FIG.4 according to an example of the present invention. Note that theillustrations of the upper and lower support pillars are omitted in (A)to (F) of FIG. 5, and the illustrations of the upper and lower framesare omitted in (E) of FIG. 5. Further, (F) of FIG. 5 is a top plan viewof (E) of FIG. 5. FIG. 6 is a process drawing for explanation of aproblematic point of a conduction heating apparatus according to acomparative example in which a clamping distance L is fixed.

[Clamping Process]

Referring to (A) and (B) of FIG. 5, the work W is held by holdingmembers 53 of the pair of parallel arms 51 which the transfer mechanism5 has, and the work W is conveyed to the energizing position P1 of theconduction heating apparatus 3 shown in FIG. 2A by the cylinders 52 a,to be placed on the pair of lower clamps 30 b and 31 b. Next, after thepair of parallel arms 51 is spaced from each other by the cylinders 52c, the pair of parallel arms 51 is lifted up by the cylinders 52 b,thereby delivering (hand over) the work W to the side of the conductionheating apparatus 3.

Referring to (C) and (D) of FIG. 5, the upper clamps 30 a and 31 a ofthe stationary clamping member 30 and the movable clamping member 31 atthe lifted-up position are lifted down by the lifting up/down cylinder32. In accordance with this operation, on the side of the stationaryclamping member 30, one side of the work W is clamped to be held at afixed position by the pair of upper and lower clamps 30 a and 30 b, toperform positioning of the work W, and on the other hand, on the side ofthe movable clamping member 31, the other side of the work is clamped tobe held by the pair of upper and lower clamps 31 a and 31 b. Note thatthe initial clamping distance is set to “L”.

Note that separate cylinders for setting or keeping the initialpositions of the pair of upper and lower clamps 30 a and 30 b of thestationary clamping member 30 may be respectively connected to the pairof upper and lower support pillars 39 a and 39 b. Note that, in place ofthese cylinders, a servo motor or the like capable of performingpositioning may be employed.

[Conduction Heating Process]

The lower clamps 30 b and 31 b spaced from each other in thelongitudinal direction of the work W serve as electrodes as well, andenergization (conduction) to the work W is started through the pair ofthe lower clamps 30 b and 31 b. Note that portions of the upper clamps30 a and 31 a for clamping the work W are formed to be convex curvedshapes, and portions of the lower clamps 30 b and 31 b for clamping thework W are formed to be planar shapes, thereby improving its clampingperformance and bringing about uniform heating.

Further, by use of the bar-shaped clamps and bar-shaped electrodes withsufficient lengths along the width direction of the work W and theconveying direction of the work are used as the upper and lower clamps30 a, 30 b, 31 a, and 31 b, the clamping performance is improved anduniform heating is expected. The widths of the clamps 30 a, 30 b, 31 a,and 31 b are set to be the same as the width of the work W or longer toa certain extent than the width of the work W, and in the case where thewidth of the work W is set to be longer, it is preferably set to belonger by approximately several % to 20%.

[Tension Applying Process in Conduction Heating Process]

Referring to (E) and (F) of FIG. 5, as an energizing time proceeds, anenergizing current is accumulated, or a temperature of the work Wincreases, during conduction heating, the pair of upper and lower clamps31 a and 31 b of the movable clamping member 31 gradually move towardthe end portion in the longitudinal direction of the work Wsynchronously with a length of stretching of the work W thermallyexpanding while holding the other side of the work W, by the upper andlower tensioning cylinders 33 a and 33 b. Thereby, making tension act onthe work W forward the moving direction of the movable clamping member31. Further, a clamping distance at the termination of conductionheating is elongated to be “L+” relative to the clamping distance “L” atthe start of conduction heating. That is, in conduction heating, aclamping distance is elongated by a stretched length of the work W,i.e., an amount of “L+”-“L”. Note that, given that the distance betweenthe clamping position by the upper and lower clamps 31 a and 31 b andthe left end of the work W in the drawing at the start of conductionheating in (D) of FIG. 5 is “D”, and the distance between the clampingposition by the upper and lower clamps 31 a and 31 b and the left end ofthe work W in the drawing at the termination of conduction heating in(E) of FIG. 5 is “E”, “D” and “E” are the same length, or “E” that is adistance after thermal expansion is slightly longer than “D” that is adistance before thermal expansion.

In this way, according to the conduction heating apparatus according toan example of the present invention, since it is possible to alwaysapply appropriate tension to the work W stretching according to atemperature rise at an appropriate clamping position during conductionheating, drooping of the central portion of the work W due to conductionheating is prevented as much as possible.

In contrast thereto, according to the conduction heating apparatusaccording to the comparative example shown in FIG. 6, the two clampingpositions are fixed, and the clamping distance between the both is “L”which is constant. That is, since the positions of tying up the bothends in the longitudinal direction of the work W are invariable, it isimpossible to continue to apply effective tension to the work Wstretching according to a temperature rise during the conductionheating, which causes its central portion to droop or warp upward.

INDUSTRIAL APPLICABILITY

The conduction heating apparatus according to the present invention issuitably built into a hot press forming apparatus, in particular, a diequenching apparatus. Further, the conduction heating apparatus and theconduction heating method according to the present invention are appliedto heating of a plate material made of metal to be hot press formed, andin particular, of a lengthwise plate material. In detail, the conductionheating apparatus and the conduction heating method according to thepresent invention are applied to heating of vehicle parts requiring massproductivity before forming, for example, heating of various types ofreinforcing members for vehicle bodies, in particular, door beams,bumper reinforcements, and the like before hot press forming.

The modifications and adjustments of the exemplary embodiment andexample are possible within the scope of all the disclosures (includingthe claims) of the present invention, and further on the basis of thebasic technical concept. Further, a wide variety of combinations andselections of various disclosed elements are possible within the scopeof claims of the present invention.

EXPLANATION OF SIGNS

-   1 Hot-press forming apparatus-   2 Feeding mechanism-   3 Conduction heating apparatus-   4 Hot press mechanism-   5 Transfer mechanism-   6 Control mechanism-   7 Conveying conveyor-   30 Stationary clamping member-   30 a, 30 b Upper and lower clamps-   31 Movable clamping member-   31 a, 31 b Upper and lower clamps-   32 Lifting up/down cylinder (lifting up/down direction driving    mechanism)-   33 a, 33 b Upper and lower tensioning cylinders (movable clamping    member driving mechanism, clamping distance varying mechanism)-   34, 34 Upper and lower translatory guides-   (30, 31, 32, 33 a, 33 b, 34) Clamping mechanism-   35 Support rod-   36 a Current sensor-   36 b Temperature sensor-   36 c Lifting up/down position sensor-   36 d Movable clamping member position sensor-   36 e Control board (control means, microcomputer)-   37 Energizing mechanism (Conducting mechanism)-   37 a Energizing switch (Conducting switch)-   38 a, 38 b Upper and lower frames-   39 a, 39 b Upper and lower support pillars (support members)-   41 Die, Cooling die-   51 A pair of parallel arms-   52 a to 52 c Cylinders (driving means)-   53 a to 53 c Holding members (clamps, holding means)-   54 Support bar-   L, L+ Clamping distances-   P Power source-   P0 Feeding position-   P1 Energizing position (Conducting position)-   P2 Processing position-   P3 Discharging position-   W Work-   D Distance between variable clamping position and left end of work W    in the drawing at the start of energization-   E Distance between variable clamping position and left end of work W    in the drawing at the termination of energization

1. A conduction heating apparatus that performs conduction heating ontoa work to be hot press-formed while clamping the work by a clampingmechanism under application of tension to the work, wherein the clampingmechanism comprises: a stationary clamping member which clamps one sideof the work to freely hold the one side of the work, and is fixed inposition or capable of being freely fixed in position along apredetermined direction, and a movable clamping member which clamps theother side of the work to freely hold the other side of the work, and tofreely move along the predetermined direction; and wherein in conductionheating, the stationary clamping member holds the one side of the workat a fixed position, and the movable clamping member moves along thepredetermined direction while holding the other side of the workaccording to a thermal deformation along the predetermined direction ofthe work to apply tension to the work.
 2. The conduction heatingapparatus according to claim 1, wherein; the clamping mechanismcomprises: a lifting up/down direction driving mechanism that drives thestationary clamping member and the movable clamping member to freelylift up/down along a thickness direction of the work to clamp the work,and a movable clamping member driving mechanism that drives the movableclamping member to freely move along the predetermined direction.
 3. Theconduction heating apparatus according to claim 1, wherein thestationary clamping member and the movable clamping member respectivelyhave pairs of upper and lower clamps facing each other along thethickness direction of the work to freely pinch the work.
 4. Theconduction heating apparatus according to claim 3, wherein the lowerclamps spaced from each other along the predetermined direction, amongthe pairs of upper and lower clamps which the stationary clamping memberand the movable clamping member respectively have, are a pair ofelectrodes for energizing the work.
 5. The conduction heating apparatusaccording to claim 3, wherein portions of the upper clamps pinching thework are of convex curved shape, and portions of the lower clampspinching the work are of planar shape.
 6. The conduction heatingapparatus according to claim 1, comprising a droop preventing memberwhich is disposed beneath a central portion of the work duringconduction heating, the droop preventing member freely supports thecentral portion.
 7. The conduction heating apparatus according to claim6, wherein the droop preventing member is a plurality of pins providedupright along the vertical direction.
 8. A conduction heating apparatusthat performs conduction heating onto a work to be hot press-formedwhile clamping the work by a clamping mechanism under application oftension to the work, wherein the clamping mechanism comprises: first andsecond clamping members that clamp the work at different clampingpositions, respectively, to apply tension to the work; a clampingdirection driving mechanism driving the first and second clampingmembers to clamp the work; and a clamping distance varying mechanismvarying a clamping distance between the first and second clampingmembers according to a thermal deformation of the work upon conductionheating.
 9. A hot press forming apparatus comprising: the conductionheating apparatus according to any one of claim 1; and a hot pressmechanism that hot press-forms the work heated by the conduction heatingapparatus.
 10. A conduction heating method for performing conductionheating onto a work to be hot press-formed while clamping the work underapplication of tension to the work, the method comprising: clamping forapplying tension to the work while clamping one side and the other sideof the work, respectively, to hold the work; conduction heating forperforming conduction heating onto the clamped work; and applying atension in the conduction heating by clamping the one side of the workat a fixed position and moving the other clamping position of the workalong with the work thermally deforming upon the conduction heating. 11.The method according to claim 10, comprising: clamping one side of thework to freely hold the one side of the work, and at a fixed position ina predetermined direction; clamping the other side of the work to freelyhold the other side of the work, and to freely move along thepredetermined direction; wherein; in conduction heating, the one side ofthe work is clamped at a fixed position, and the movable clamped sidemoves along the predetermined direction while holding the other side ofthe work according to a thermal deformation along the predetermineddirection of the work to apply tension to the work.
 12. The methodaccording to claim 10, further comprising: driving the stationaryclamping member and the movable clamping member so as to freely liftup/down along a thickness direction of the work to clamp the work; andmovably clamping the movable clamped side so as to freely move along thepredetermined direction.
 13. The method according to claim 10, whereinthe stationary clamping and the movable clamping respectively areperformed by pairs of upper and lower clamps facing each other along thethickness direction of the work to freely pinch the work.
 14. The methodaccording to claim 13, wherein the lower clamps spaced from each otheralong the predetermined direction, among the pairs of upper and lowerclamps which the stationary clamping member and the movable clampingmember respectively have, serve as a pair of electrodes for energizingthe work.
 15. The method according to claim 13, wherein portions of theupper clamps pinching the work are of convex curved shape, and portionsof the lower clamps pinching the work are of planar shape.
 16. Themethod according to claim 10, wherein a central portion is supported bya droop preventing member which is disposed beneath a central portion ofthe work during conduction heating, thereby preventing droop of thecentral portion of the work.
 17. The method according to claim 16,wherein the droop preventing member comprises a plurality of pinsprovided upright along the vertical direction.
 18. A hot press formingmethod comprising: the conduction heating method according to claim 10;and hot press-forming the work heated by the conduction heating toproduce a hot-press-formed product.
 19. A hot press forming apparatuscomprising: the conduction heating apparatus according to claim 8; and ahot press mechanism that hot press-forms the work heated by theconduction heating apparatus.